Various methods of manufacturing ridge waveguide structures have previously been proposed. For example, the Kaminow method which uses standard processing with two-step photolithography, a first step to define double channels in, for example, a standard double heterojunction layer structure between which the ridge is disposed and a second step to open contact windows to the ridge. The ridge is electrically isolated from the remainder of the layer structure by silicon dioxide which is deposited to cover the entire device, and extends into the channels, following ridge definition and in which the contact windows to the ridges have to be subsequently opened. An alternative method involves only a single photolithographic step and a lift-off technique. In this method a standard double heterojunction layer structure is provided with a silicon dioxide layer on the cap layer and successive layers of titanium and gold deposited thereon. Using the single photolithographic step a window is provided in a photoresist layer the gold is etched via this window so that the photoresist is undercut. The titanium and silicon dioxide are then etched, the extent of the gold etching meaning that these layers are also etched a greater extent than exposed by the window. Successive layers of titanium and gold are then deposited over the photoresist during which process ridge contact layers of titanium and gold are built up in the undercut recess via the window and of dimensions determined by the window. The photoresist is then removed, simultaneously lifting off the titanium and gold layers deposited thereon, and the double channels etched using the structure produced so far to provide its own masking (self-aligned) to produce the full ridge structure which is already contacted. This method of manufacture results in the disadvantage that the sides of the doubles channels are not insulated and there is the possibility of short circuits when the devices have connections soldered thereto.